Bright-dark pulse pair and soliton bunch generation from mode-locked erbium-doped fiber laser with GIMF-SIMF-GIMF as a saturated absorber

Abstract

We demonstrated an experimental observation of bright-dark pulse pair and soliton bunch in mode-locked erbium-doped fiber ring laser with the saturable absorber (SA) of graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF), which utilizes nonlinear multimode interference inside the multimode fiber to realizing mode locking of fiber laser. During the experiment, we observed a fascinating phenomenon of dualwavelength bright-dark pulse pair, in which the wavelengths of the two wavelengths are 1558.5 nm and 1560.1 nm, respectively, and the wavelength interval is 1.6 nm. The PBS filter was used to verify that the bright and dark pulses are orthogonal to each other in polarization. We also obtained multiple set of soliton bunches running at the fundamental frequencies of 100.5 ns, and when we increase the pump power we could find that the number of optical solitons increases in a single soliton bunch, which experimental phenomenon is in appropriate agreement with the theory. Based on the observation and understanding of these experimental phenomena, it is beneficial to explore the rich nonlinear effects in the mode-locked fiber laser.